Zero Threshold Reactions for Detecting Cosmic Relic Neutrinos R. S. Raghavan Virginia Tech

Zero Threshold Reactions for Detecting Cosmic Relic Neutrinos

R. S. RaghavanVirginia Tech

XII Neutrino TelescopesVenice March 9 2007

Be

Beginnings: Important influences:

Zero Threshold Reactions (ZTR)Weinberg Paper 1962:

Inference:

All weak interaction reactions (EC, β− , β +) are affected by the CRN. Their normal decay rates are modified by additionalMode of decay induced by CRN species anti to that emitted in normal decay

CRN

Normal Decay

A(Z) A(Z+1) + e- + νe

RSRaghavan Virginia Tech: XII Nu telescopes Venice Match 9 2007

II. Long interest in νe reactions

with thresholds << 1.8 MeV (geoneutrinos etc)

In particular the 1 MeV addition due to positron emission

L Mikaelyan (1968) showed the way…. Induced Electron Capture-- IEC

σ (IEC) ≈ 0 unless E(νe) = Q(EC).

Resonance Reaction

A(Z)

A(Z-1)

ECIEC

QEC

Γ


Resonance Density= No of nu’s in beamPer unit energyAt the resonance energy

Width of final stateh / τ = mean life

= deBroglieWavelength ofIncidentneutrino = h/p

Cross section for IEC---Resonance reaction—Apply Resonance Theory

Γ contains all weak interaction properties

σ (IEC) ≈ 0 unless E(νe) = Q(EC).within Γ very difficult sinceΓ very very narrow for weak decays

No progress since 1968 since no sourceof resonant νe could be found


Idea III. Bahcall 1963 Bound state beta decayTake source of beta decay—not normal one where e goes into thecontinuum but is captured in a bound orbit— bound state beta decay !(0.5% in tritium)

In this case the νe energy is at exactly –I mean Exactly at resonance—Emission & Absorption areExact time-reversed processesResonant capture of antineutrinos—Exact resonance is still impossible unless theνe is emitted and absorbed WITHOUT RECOIL (RSR 2005)Moessbauer neutrinos ! (still --many solid state problems now in technical development )

2005 (RSR)—Yes there is !

A(Z) A(Z+1) + e- + νe

A(Z)

IECQEC

Γ


νe

A(Z)

A(Z-1)

EC QEC

Γ

Induced Decay?What happens when νe

is applied not to the daughter to excite it but to the radioactive PARENT to persuadeit to decay?

Same formula can be appliedIn this case the reaction threshold is ZEROAny neutrino can induce decaycosmic relic nu of ultra-low energy


Radiative EC decay induced by CRN

νe

A(Z)

A(Z-1)

EC QEC

Γ

γ

Competes with normalradiative EC (Internal BremmstrahlungKnown since 1940—Morrison & Schiff))


CRN induced Radiative EC

ωγ / ωK radiative fraction of K-EC decay—photon coupling is the same as in normal IB emissionωγ / ωEC = (α/12π) Q2 (Bambynek et al RMP 49, 77, 1977)

We have now everything to understand rates of the CRN effect and the unshieldable background due to internal bremmstrahlung


This formula displays new general physical insights for CRN-induced decay Every nu in beam can induce decayρ (spectral density for interaction/incident nu = 1/eV if Γ (in eV)σ determined by λ the deBroglie wavelength of incident CRN—key pointMomentum of CRN are very small –smallest of known Nu’sσ (CRN effect) is largest for CRN than for any other known Nu !

Nature provides a rare break for nu physics & cosmology

= h / τ (s)


Rates, background….

• CRN Source: number density, motion of earth in galaxy

Assume mνc2 = 1 eV: Nν is only for νe

For earth v = 10-3 c


K [mν c2 / (v/c)] fK


Signal: “Monoenergetic” line just above endpoint

Background:

Unavoidable background —Internal Bremmstrahlung just below end point

(in mc2 units)


Illustration: EC decay of 37Ar

Target factor is fK = ft / t


Typical experimental numbers for 37Ar andImplications for nu mass


Exactly same considerations for β+ and β- decaysexcept: Drop the photon coupling factor

K improves by x103 Mainly because 10-4 photon factor is absent

Positron Decay:


mνc2 sensitivity a few meV


t

Tritium case very unfavorable because f is so low (v low energy ~18 keV) for T decay


For better case, go to high energy decays—short lifetimesCan apply continuous beams of radioactive species

Example: 6He —Q~ 3.5 MeV t1/2 ~1 s: production e.g. 9Be(n,α)In a powerful nuclear reactor—exctract beam by boiling off He.

Mass sensitivity few meV

6He beams (100 μamp, 1018 He/year ( mega Curie Equivalents) are being produced in beta-beam development. Technology available now.


New: Signatures for CRN effect

For a given target, size of effect depends on the Neutrino Momentum in the experiment. If the momentumIs controllable, the effect can be controlled.Example: Ar source experiment

Vearth in galaxy 300 km/s

Vearth rotation 30 km/sec

±10% daily sinusoidal variation of p 20% max variation Of signal every day with time of day Easily detectable


Additional Signatures:kinematic control in beam experiments

Precision velocity control necessary—< 1 keV (~ galaxy motion)Δv << 1 keV May be possible to explore mass structure of neutrinoThe e-flavor is present in different proportions in each mass eigenstate that move with different momentaThe size of the CRN effect will increase and decreaseAs the correct velocity is scannedcomplete PMNS matrix ( is there a θ13 ? Since m3

is much more separated than 1 and 2.Heavier neutrinos of any kind (sterile?)

Earth motions completely cancelled –natural CRN FD spectrumAbsolute energies from absolute beam velocities


Conclusions

•Experiments (Ar, O, He) are all within reach of state of the art Technology Nuclear Physics (beams, source production, beta spectrometers,Ge detectors (GammaSpheres), Bent Crystal Spectrometers (ΔE~0.2 eV)……•Target selection is not very restrictive—Many possibilities•Beams of Light nuclei easily produced and manipulated

Cautious view of ONE experimentalist:Future for CRN science and spectroscopy appears not so dim!


Zero Threshold Reactions for Detecting Cosmic Relic Neutrinos R. S. Raghavan Virginia Tech

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